ORDER ACQUISITION BY CLAY PLATELETS IN A MAGNETIC-FIELD - NMR-STUDY OF THE STRUCTURE AND MICRODYNAMICS OF THE ADSORBED WATER LAYER

Suspensions of the Ecca Gum BP bentonite in heavy water are oriented by the magnetic induction field in the probe of an NMR spectrometer. Ordering of the clay platelets is a slow (minutes to hours) cooperative process. It gives rise to residual quadrupolar splittings for H-2 and O-17 nuclei within the water solvent. Binary mixtures of D2O with acetonitrile-d3, acetone-d6, dimethyl-d6 sulfoxide, and methanol-d4 likewise display splittings of the CD3 deuteron resonance, from the orientation of the clay particles in the magnet. The coexistence for the deuterons in D2O of paramagnetic relaxation and of quadrupolar relaxation pathways shows as differential line broadening for the two components of the doublet. A sign reversal even occurs in going from a sodium-rich to a calcium-rich clay! The results are analyzed for the order parameters characteristic of water molecules at the clay interface.